Electronics systems are typically organized by mounting various system components on printed wiring boards and interconnecting the printed wiring boards with a circuit transmission component known as a backplane. As the circuit density of printed wiring boards increases, it becomes increasingly difficult to provide the needed backplane interconnections because, as interconnection transmission lines become thinner, their impedances increase. Moreover, the distance over which information must be transmitted by backplane conductors is normally fairly long compared to the distances transmitted on the printed wiring boards. These factors may reduce the speed at which circuits can be operated, which may defeat a principal advantage of higher circuit densities.
The copending applications of Holland et al., Ser. No. 07/785,112, field Oct. 30, 1991, now U.S. Pat. No. 5,155,785, granted Oct. 13, 1992, and Bonanni et al., Ser. No. 07/757,870, filed Sep. 11, 1991, now U.S. Pat. No. 5,204,925, granted Apr. 20, 1993, hereby incorporated herein by reference, describe the use of "optical" backplanes comprising optical fibers mounted on a substrate for interconnecting printed wiring boards. The electrical energy of each printed wiring board is translated to optical energy which is transmitted by an optical fiber on the optical backplane to another printed wiring board where it is translated back again to electrical energy for transmission on the other printed wiring board. Because optical fibers can transmit much greater quantities of information than electrical conductors, and with significantly less loss, such optical backplanes have a promising future. They could, of course, also be used to interconnect optical wiring boards, that is, circuit components on which signals are transmitted optically, and other electrical circuit modules such as multi-chip modules and hybrid integrated circuits.
Even though the use of optical backplanes tends to simplify the interconnection problem, the optical fiber interconnections on a backplane may still be very complex and relatively difficult to fabricate. There has therefore been a long-felt need in the industry for methods for fabricating optical fiber backplanes that are amenable to mass production, that reduce the operator skill required for fabrication, and in which the optical fiber lengths are adequately precise. In many modern digital systems, deviations in optical fiber length may result in timing and synchronization errors. Various machines are available for automatically routing and bonding electrical wire to a substrate, but, in general, these machines cannot be adopted for optical fiber use because of the relative fragility of optical fiber and its relative inability to withstand heat and pressure, abrupt turns, etc.